1. Field of Inventions
The present inventions relate generally to devices that are used to introduce diagnostic and therapeutic apparatus into the body.
2. Description of the Related Art
There are many instances where physicians must introduce diagnostic and therapeutic apparatus, such as diagnostic and therapeutic electrodes, ultrasound transducers, biopsy devices and other surgical tools, into the body. The diagnostic and therapeutic apparatus are often carried by catheters, which allow physicians to gain access to the body in a minimally invasive manner by way of bodily lumens. In cardiac treatment, for example, a catheter is advanced through a main vein or artery into the region of the heart that is to be treated.
One method of introducing diagnostic and therapeutic apparatus into the body is to introduce a tubular member (typically a “sheath”) into the vicinity of the targeted region. A diagnostic or therapeutic apparatus is then passed through the tubular member to the targeted region. If necessary, the diagnostic or therapeutic apparatus may be removed after its function is performed, but the tubular member left in place, so that other apparatus may be advanced to the targeted region to complete the diagnostic and/or therapeutic procedure.
Precise placement of the diagnostic or therapeutic apparatus is very important, especially in those procedures concerning the heart. To that end, some conventional sheaths are guided to the targeted region with a steerable catheter that is located within the sheath lumen. Once the sheath reaches the targeted region, the steerable catheter is removed from the sheath and a catheter carrying the diagnostic or therapeutic apparatus is advanced through the lumen. This type of sheath lacks any onboard steering mechanism. As a result, redeployment of the distal portion of sheath, even to a region in close proximity to the initially targeted region, requires the withdrawal of the diagnostic or therapeutic apparatus and the reintroduction of the steering catheter.
Other conventional sheaths include a steering mechanism that allows the physician to deflect the distal portion of the sheath. The steering mechanism consists primarily of one or more steering wires. One end of each steering wire is secured to the distal end of the sheath, while the other end is secured to a steering control device, such as the rotating cam and steering control knob arrangement commonly found in steerable catheters. Rotation of the control knob causes one of the wires to impart a pulling force on the distal portion of the sheath, thereby causing the distal portion to deflect. To promote steerability, the distal portion of the sheath (which is relatively short) is typically formed from relatively soft, flexible material. Conversely, the proximal portion (which is relatively long) is formed from relatively hard, less flexible material that provides better torque transmission properties.
The inventors herein have determined that there are a number of shortcomings associated with conventional steerable apparatus, such as steerable sheaths, that are used to introduce diagnostic and therapeutic apparatus into the body. For example, it is desirable to provide a sheath or other tubular member having a small outer diameter (OD) in order to limit the size of the entry hole that must be made in the patient's vein or artery and to compensate for the effects of arteriosclerosis. Because the diameter of the lumen, or inner diameter (ID), tends to be a function of the size of the diagnostic and therapeutic apparatus to be introduced into the body, the primary method of reducing the OD is reducing the wall thickness of the tubular member.
Heretofore, efforts to reduce wall thickness have been hampered by the fact that the wall strength of the tubular member distal portion must be sufficient to prevent the steering wire from tearing through the distal portion during deflection. Proposed solutions to the strength problem included the use of harder materials and/or the addition of mechanical devices, such as coils, to the distal portion of the tubular member. The inventors herein have determined that such solutions are less than optimal because they limit the flexibility and, therefore, the steerability of the distal portion of the sheath or other tubular member.
The inventors herein have also determined that the distal portion of the tubular member in conventional steerable apparatus will sometimes buckle during steering operations and do not always return to the neutral position after the steering operation is complete. Moreover, it can be difficult to produce a distal portion that will bend to a specific radius of curvature using conventional structures and manufacturing techniques.